BY W. N. BENSON. 619 



Jittle doubt that the vesicle was filled with magmatic water. It 

 would seem that the jelly-like mother-liquor in the vesicles per- 

 mitted the growth of well. formed prisms of augite, which were 

 pushed aside by the growing and mutually interfering spherical 

 masses of natrolite and opal, in the outer portion of which the 

 augites become imbedded. The growth of large idiomorphic 

 crystals of ferromagnesian minerals in the concentrations of the 

 residual magmatic water is analogous in some respects to the 

 formation of barkevicite in the analcitic luffarites of the Glassrow 

 district described by Tyrrell(31). Jt is also interesting as afford- 

 ing a good instance of the primary nature of a zeolite, upon 

 which subject a considerable literature has accumulated in recent 

 years. [See e.g.^ Mr. Barker's Presidential Address(32), and the 

 article (and bibliography) by Koenigsberger(33)]. Beside the 

 vesicles, there are small veins and irregular patches of opal and 

 natrolite, and a little radiating aggregate of augite illustrated in 

 'J'ext-fig. 15B. In addition to these, there are also present a xeno- 

 lith of olivine, augite, anorthite, and picotite, and isolated grains 

 of the same minerals. Such xenoliths and xenocrysts are com- 

 monly present in the Tertiary and Recent basalts throughout the 

 world. 



Summary. 

 The main results of the present work may be stated thus. A 

 more detailed map has been made of the Tamworth district, than 

 that given by the previous authors who studied the district, and the 

 subdivision of the Devonian Series instituted elsewhere in the Ser- 

 pentine Belt has been applied, with amplifications, to this district. 

 The result has been a general confirmation of the earlier work, 

 with some modification in the details. The history of the area was 

 apparently as follows. In Devonian times, a series of radiolarian 

 claystones was deposited on a steadily sinking sea-floor, which was 

 maintained at a fairly shallow depth. During this period, there 

 were great developments of volcanic activity, producing large 

 amounts of pyroclastie matter, building masses of tuff and agglo- 

 merate, which, here and there, may have risen above the surface 

 of the sea, as small, short-lived islands. There were two main 



